Gamma-Ray Observations of the Galactic Center and Some Possible Point Sources

Abstract

A (.5 m by .5 m) digitized spark chamber gamma ray telescope was flown on three balloon flights to look at the galactic center region, Virgo, and the Crab. An excess flux above atmospheric background of over four standard deviations was found for gamma rays exceeding 100 MeV coming from the galactic center region, corresponding to a line intensity of (2.0 +0.6) x 10 -4 y's(cm2 rad see),but there was no statistically significant excess in the 50 to 100 MeV interval, with a 95% confidence limit for the ratio EJ(50 -100 MeV) /J(> 100 McV)]being 0.50. As a result, there is only a 6% chance that Compton or synchrotron radiation from electrons with a power law spectrum having an exponent of 2.6 could make as much as a 50% contribution to the gamma radiation in this energy range. No positive evidence was found for radiation from any of the sources M 87, 3C273, and the Crab Nebula, and 95% confidence upper limits for the gamma ray flux from these objects were set at 1.0 . 10 -5 , 1.0 . 10 -5 , and 6 . 10 -5 /(cm 2 sec) respectively. The M-87 limit eliminates the possibility that the power law spectrum observed at X-ray energies extends unchanged to the high energy gamma ray region.

High-energy gamma-ray results from the second small astronomy satellite

“…Nonetheless, data from these at high energies (? 100 MeV), some positive results and other upper limits (Frye et al, 1971;Bennett et al, 1972;Fichtel et al, 1972;Dahlbacka et al, 1973;Sood et al, 1974;Frye et al, 1974), agree with the results shown in figure 9 within rather large uncertainties, except Frye et al (1974), who report values well below those shown.…”

SAS-2 Observations of the High-Energy Gamma Radiation from the VELA Region

“…given by Fichtel et al (1973), a more complete description of the detector system by Derdeyn et al (1972), and a discussion of calibration and data analysis procedures by Fichtel et al (1972) and Thompson (1973). During the period February 15 to 20, 1973, the region of the sky including the galactic plane from II = 2500 to II = 2900 was examined.…”

Celestial Diffuse Gamma Radiation above 30 MeV Observed by SAS-2

“…A more complete discussion of the SAS-II gamma ray telescope is given by Derdeyn et al (1972). The calibration and data analysis are similar to that used for previous balloon gamma ray digitized spark chambers (Fichtel et al, 1969;Kniffen, 1969;Fichtel et al, 1972;and Thompson, 1973).…”